Just minutes after officially becoming Prime Minister, Mrs May gave Mr Johnson one of the most powerful roles in government and also removed George Osborne as chancellor without offering him an alternative job.

Theresa May with her husband PhilipCredit:
EPA

It came after she gave a speech on the steps of Downing Street in which she vowed to “fight against burning injustice” in Britain and build “a country that works for everyone”.

In her first address to the nation, she instantly distanced herself from David Cameron’s government by declaring she would not “entrench the advantages of the fortunate few”.

Mr Johnson last night said he was "very humbled, very proud to be offered this chance". He said he was "very, very surprised" to have been offered the job of Foreign Secretary, adding: "You could have knocked me down with a feather."

He added: "Clearly we now have a massive opportunity to play a new part in Europe to make a great success of our new relationship with Europe and the World. I'm very excited to play a part of that."

Asked if he will apologise to Barack Obama after criticising him for warning about the risks of Brexit by saying Britain would go "to the back of the queue" in any trade negotiations, Mr Johnson said: "The United States will be at the front of the queue."

The appointment of senior Leave campaigners was welcomed by Tory backbenchers and Eurosceptics, who said it was proof that Mrs May, who supported staying in the EU, will stick to her promise that “Brexit means Brexit”.

Nigel Farage, the former UK Independence Party leader, praised the “inspired choices” and said he was now “more optimistic” that the vote to leave the EU would be followed through.

The dramatic events began just over an hour after Mr Cameron left Downing Street for the last time, accompanied by his family.

In his emotional final address to the public, Mr Cameron said that he believed he was leaving the country “much stronger” and the economy “immeasurably stronger” after his six years in office.

David Cameron speaks with the press before leaving 10 Downing Street for the last time as wife Samantha and children Nancy, Arthur and Florence look onCredit:
Getty Images

Flanked by his wife, Samantha, and children Nancy, Elwen and Florence, he spoke of his pride at reducing the deficit, introducing same-sex marriage, increasing international aid spending and cutting waiting times for NHS treatment.

He paid tribute to his wife, whom he described as “the love of my life” who had “kept me vaguely sane”.

Earlier, Mr Cameron had received a standing ovation from his backbenchers after completing his final appearance at Prime Minister’s Questions.

After warm tributes from MPs from all parties, Mr Cameron ended his farewell by telling the Commons: “I was the future once.”

He then returned to Downing Street, where he left two bottles of red wine for Mrs May in her new office, before his final departure. On Tuesday night he held a “last supper” in Downing Street for 25 aides, friends and family members.

Mrs Cameron gave an emotional speech in which she said that “what people don’t realise is just what happy times the last six years have been”.

When we take the big calls, we’ll think not of the powerful, but you.Theresa May

As she became Britain’s second female prime minister after Margaret Thatcher just before 6pm, Mrs May said that her new Government will do “everything we can to help anybody, whatever your background, to go as far as your talents will take you”.

Minutes after meeting the Queen in Buckingham Palace, she directly addressed hard-working people and told them: “We will prioritise not the wealthy, but you.”

She said that Britain will “rise to the challenge” of Brexit and pledged to build a “bold, new positive role for ourselves in the world” outside the European Union.

Distancing herself from the administration led by Mr Cameron and Mr Osborne, she said: “The government I lead will be driven not by the interests of the privileged few, but by yours. We will do everything we can to give you more control over your lives.

“When we take the big calls, we’ll think not of the powerful, but you. When we pass new laws, we’ll listen not to the mighty, but to you.

"When it comes to taxes, we will prioritise not the wealthy, but you. When it comes to opportunity, we won’t entrench the advantages of the fortunate few.”

With her husband, Philip, standing behind her, she said that for an “ordinary working-class family” life is “much harder than many people in Westminster realise”.

Her speech highlighted her clear intention to reach out to Labour voters who feel alienated by Jeremy Corbyn and to reclaim the centre ground of British politics.